22 Aug
2002
22 Aug
'02
2:35 a.m.
Jim Battle wrote:
2) This one is a reverse job. The microcode board has
quite a few mask
ROM chips. I don't care what the actual part number is, but I'm
hoping someone will say, "hey, that pinout is just like a ..." so that
I can find a prom programmer to read the thing. If I have to, I guess
I could build a parallel port dongle to read them. Here's what I
know:
24 pins
data out on pins 16-23
pin 1 is +5V
pins 2-8, 10, 11, 13, 15 are the address pins
pin 14 is either a chip select or output enable; active low
pins 12 and 24 are pulled up to +5; chip selects maybe?
pin 9 might be -15V (!)
Embarrassingly, I can't find a connection to GND. unfortunately, I
don't know the backplane connections either, so I can't identify if
pin 9 is really -V or just an alternate ground (but I see a bypass cap
between the digital ground and this net, so it makes me think).
PMOS parts typically ran on a single supply of around 12-15V. For TTL
compatability, it was common to run them from +5V and -9V, with noground.
+5V and -15V would effectively provide a 20V supply, which is more than
was typical with PMOS, but not completely out of the question.
One more thing, the manufacturer's logo and part
prefix are "EA".
"Electronic Arrays". They were pretty big in masked ROMs and keyboard
encoders at one time. I'm not sure what eventually happened to them,
but they were probably acquired by someone else.